We develop a new theoretical framework for the treatment of heavy quark (HQ) resonances within heavy quark effective theory (HQET). This framework uses on-shell recursion techniques to express the resonant amplitude as a product of on-shell subamplitudes, which allows one to employ a form-factor representation of the hadronic matrix elements and to obtain an HQ expansion, but at the price of introducing complex momenta. We construct a generalized “holomorphic HQET” onto which such complex-momentum matrix elements can be matched, and we show that $\textit{PT}$ symmetry ensures the Isgur-Wise functions (and the perturbative corrections) become holomorphic functions of the complex recoil parameter with real coefficients. They are thus an analytic continuation of the standard HQET description. This framework admits a HQ hadron (strong decay) width expansion. At second order, we show it is compatible with data for the $$ {B}_{1(2)}^{\left(\ast \right)} $$ and $$ {D}_{1(2)}^{\left(\ast \right)} $$ HQ doublets. Taking the $$ \overline{B}\to \left({D}_1^{\ast}\left({1}^{-}\right)\to D\pi \right) l\nu $$ system as an example, we compute the holomorphic HQET expansion to first order, as well as the complex-momentum on-shell subamplitudes. A toy numerical study of the resulting differential rates demonstrates that this framework generates HQ resonance lineshapes with large tails, resembling those seen in data.

United States

Claudio Manzari

Dean Robinson

On-shell recursion and holomorphic HQET for heavy quark hadronic resonances

The type-I seesaw model is probably the most straightforward and best studied extension of the Standard Model that can account for the tiny active neutrino masses determined from neutrino oscillation data. In this article, we calculate the complete set of one-loop corrections to charged lepton flavour violating processes within this model. We give the results both using exact diagonalisation of the neutrino mass matrix, and at leading order in the seesaw expansion (i.e.   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (v 2 /   <math> <msubsup> <mi>M</mi> <mi>R</mi> <mn>2</mn> </msubsup> </math>  $$ {M}_R^2 $$ )). Furthermore, we perform the matching onto the SU(2) L  invariant Standard Model Effective Field Theory at the dimension 6 level. These results can be used as initial conditions for the renormalisation group evolution from the right-handed neutrino scale down to the scale of the physical processes, which resums large logarithms. In our numerical analysis, we study the inverse seesaw limit, i.e. the symmetry protected type-I seesaw, where the Wilson coefficient of the Weinberg operator is zero such that sizeable neutrino Yukawas are permissible and relevant effects in charged lepton flavour violating observables are possible. We correlate the different charged lepton flavour violating processes, e.g. ℓ → ℓ′γ, ℓ → 3ℓ′, μ → e conversion and Z → ℓℓ ′, taking into account the constraints from electroweak precision observables and tests of lepton flavour universality.

Switzerland

Andreas Crivellin

Fiona Kirk

Comprehensive analysis of charged lepton flavour violation in the symmetry protected type-I seesaw

The field of particle physics is at the crossroads. The discovery of a Higgs-like boson completed the Standard Model (SM), but the lacking observation of convincing resonances Beyond the SM (BSM) offers no guidance for the future of particle physics. On the other hand, the motivation for New Physics has not diminished and is, in fact, reinforced by several striking anomalous results in many experiments. Here we summarise the status of the most significant anomalies, including the most recent results for the flavour anomalies, the multi-lepton anomalies at the LHC, the Higgs-like excess at around 96 GeV, and anomalies in neutrino physics, astrophysics, cosmology, and cosmic rays. While the LHC promises up to 4  $$\hbox {ab}^{-1}$$  <math> <msup> <mtext>ab</mtext> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> </math>   of integrated luminosity and far-reaching physics programmes to unveil BSM physics, we consider the possibility that the latter could be tested with present data, but that systemic shortcomings of the experiments and their search strategies may preclude their discovery for several reasons, including: final states consisting in soft particles only, associated production processes, QCD-like final states, close-by SM resonances, and SUSY scenarios where no missing energy is produced. New search strategies could help to unveil the hidden BSM signatures, devised by making use of the CERN open data as a new testing ground. We discuss the CERN open data with its policies, challenges, and potential usefulness for the community. We showcase the example of the CMS collaboration, which is the only collaboration regularly releasing some of its data. We find it important to stress that individuals using public data for their own research does not imply competition with experimental efforts, but rather provides unique opportunities to give guidance for further BSM searches by the collaborations. Wide access to open data is paramount to fully exploit the LHCs potential.

United Kingdom

Oliver Fischer

South Africa

Bruce Mellado

Stefan Antusch

Emanuele Bagnaschi

CERN

Shankha Banerjee

Geoff Beck

Italy

Benedetta Belfatto

Matthew Bellis

Zurab Berezhiani

Germany

Monika Blanke

Bernat Capdevila

Taiwan

Kingman Cheung

India

Nishita Desai

Bhupal Dev

Rohini Godbole

Tao Han

Philip Harris

Martin Hoferichter

Matthew Kirk

Austria

Suchita Kulkarni

Clemens Lange

Finland

Kati Lassila-Perini

Zhen Liu

France

Farvah Mahmoudi

David Marzocca

Biswarup Mukhopadhyaya

Spain

Antonio Pich

Xifeng Ruan

Luc Schnell

Jesse Thaler

Susanne Westhoff

Unveiling hidden physics at the LHC

New-physics (NP) constraints on first-generation quark-lepton interactions are particularly interesting given the large number of complementary processes and observables that have been measured. Recently, first hints for such NP effects have been observed as an apparent deficit in first-row CKM unitarity, known as the Cabibbo angle anomaly, and the CMS excess in   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$  → e + e  − . Since the same NP would inevitably enter in searches for low-energy parity violation, such as atomic parity violation, parity-violating electron scattering, and coherent neutrino-nucleus scattering, as well as electroweak precision observables, a combined analysis is required to assess the viability of potential NP interpretations. In this article we investigate the interplay between LHC searches, the Cabibbo angle anomaly, electroweak precision observables, and low-energy parity violation by studying all simplified models that give rise to tree-level effects related to interactions between first-generation quarks and leptons. Matching these models onto Standard Model effective field theory, we derive master formulae in terms of the respective Wilson coefficients, perform a complete phenomenological analysis of all available constraints, point out how parity violation can in the future be used to disentangle different NP scenarios, and project the constraints achievable with forthcoming experiments.

First-generation new physics in simplified models: from low-energy parity violation to the LHC

New neutral heavy gauge bosons (Z′) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic Z′ bosons (even with sizable couplings) can be much lighter and therefore lead to interesting quantum effects in precision observables (like (g − 2)μ) and generate flavour violating decays of charged leptons. In particular,   <math> <mi>ℓ</mi> <mo>→</mo> <mi>ℓ</mi> <mo>′</mo> <mi>v</mi> <mover> <mi>v</mi> <mo>¯</mo> </mover> </math>  $$ \mathrm{\ell}\to \mathrm{\ell}^{\prime }v\overline{v} $$  decays, anomalous magnetic moments of charged leptons, ℓ → ℓ′γ and ℓ → 3ℓ′ decays place stringent limits on leptophilic Z′ bosons. Furthermore, in case of mixing Z′ with the SM Z, Z pole observables are affected. In light of these many observables we perform a global fit to leptophilic Z′ models with the main goal of finding the bounds for the Z′ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an L  μ  − L  τ  symmetry broken only by left-handed rotations, or considers the case of τ − μ couplings only. In the latter setup, on can explain the (g − 2) μ  anomaly and the hint for lepton flavour universality violation in   <math> <mi>τ</mi> <mo>→</mo> <mi>μv</mi> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mo>/</mo> <mi>τ</mi> <mo>→</mo> <mi>ev</mi> <mover> <mi>v</mi> <mo>¯</mo> </mover> </math>  $$ \tau \to \mu v\overline{v}/\tau \to ev\overline{v} $$  without violating bounds from electroweak precision observables.

Andrzej Buras

Marc Montull

Global analysis of leptophilic Z′ bosons

The “Cabibbo Angle Anomaly” (CAA) originates from the disagreement between the CKM elements V  ud  and V  us  extracted from superallowed beta and kaon decays, respectively, once compared via CKM unitarity. It points towards new physics with a significance of up to 4 σ, depending on the theoretical input used, and can be explained through modified W couplings to leptons. In this context, vector-like leptons (VLLs) are prime candidates for a corresponding UV completion since they can affect Wℓν couplings at tree-level, such that this modification can have the dominant phenomenological impact. In order to consistently assess agreement data, a global fit is necessary which we perform for gauge-invariant dimension-6 operators and all patterns obtained for the six possible representations (under the SM gauge group) of VLLs. We find that even in the lepton flavour universal case, including the measurements of the CKM elements V  us  and V  ud  into the electroweak fit has a relevant impact, shifting the best fit point significantly. Concerning the VLLs we discuss the bounds from charged lepton flavour violating processes and observe that a single representation cannot describe experimental data significantly better than the SM hypothesis. However, allowing for several representations of VLLs at the same time, we find that the simple scenario in which N couples to electrons via the Higgs and Σ1 couples to muons not only explains the CAA but also improves the rest of the electroweak fit in such a way that its best fit point is preferred by more than 4 σ with respect to the begin.

Global electroweak fit and vector-like leptons in light of the Cabibbo angle anomaly